696
AGUS74 KWCO 151507
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1007 AM CDT SUN JUN 15 2025

.Synopsis...
Small stream and flash flood potential continues for the Southern Plains
into the Lower Mississippi Valley, Mid Atlantic into the Upper Ohio Valley,
and Upper Midwest... Snowmelt runoff concerns across Northern Alaska...
Isolated flooding concerns for Puerto Rico this week...

.Southern Plains into the Lower Mississippi Valley...
Isolated flash flooding is possible today into early day 2 (Mon) across the
entire region, with the greatest chance for flooding impacts being across
the Ozarks to the ArkLaTex where potential is highest for prolonged heavy
rainfall. Portions of this region have received 2 - 4" of rainfall over the
past 3 days (MRMS), leaving them sensitive to additional/renewed flooding
impacts. Streamflows remain above normal as well (USGS), so small stream
flooding remains a concern, especially with the National Water Model (NWM)
showing potential for rapid onset flooding across the Ozarks for later this
afternoon and evening. Confidence in flooding impacts is not particularly
high, but, trends will need to be monitored closely throughout the day. New
isolated moderate river flooding is expected into day 3 (Tue) across
central OK in response to this mornings rainfall, and additional minor
river flooding will be possible across the entire region. Additionally,
isolated moderate and major river flooding will continue through mid week
across eastern TX.

.Mid Atlantic into the Upper Ohio Valley...
Flash flooding is possible today into early day 2 (Mon), especially across
southeast VA through northern NC and across eastern WV, as multiple rounds
of heavy rainfall traverse basins that saw 1 - 2"+ of rain yesterday
leaving soils primed for efficient runoff today. Heaviest rainfall totals
of 2 - 4" are possible south of Richmond towards Norfolk (VA) and into
northern NC. Intense rainfall rates will be the primary driver of flooding
impacts across the complex terrain in eastern WV today. Across both of the
aforementioned regions, locally considerable flash flooding impacts cannot
be completely ruled out today, and isolated mainstem river flooding will be
possible. The NWM short range forecast (SRF) is indicating increasing
probabilities for rapid onset flooding across eastern WV this afternoon,
some of which could be significant as suggested by the forecast flows with
4 - 10% annual exceedance probabilities in the complex terrain of the far
upper portions of the Potomac basin in WV. The NWM SRF is also showing
isolated small stream flooding potential across VA and NC as well, but with
lower areal coverage/magnitude of response. On days 2 - 3 (Mon - Tue),
periods of rain continue across the upper Ohio Valley, with particular
interest across southwest PA and WV where higher rainfall totals are
possible across some of the basins where soil moisture has increased in
response to the 1 - 2" of rain they have seen over the past 48-hours. Flash
and small stream flooding will continue to be a concern in these areas.

.Upper Midwest...
Multiple days of priming rainfall (1 - 2" cumulative totals through day 2
(Mon)) are expected across southern MN and northern/western IA (and
surrounding region) ahead of a heavier rainfall event on day 3 (Tue) into
day 4 (Wed), where another 1 - 2.5" of rainfall in a 24-hour period will
increase the flooding potential across the region. For day 1 (Sun),
isolated flash flooding will be possible across northwestern IA as multiple
rounds of heavy rainfall are likely across the same basins that saw 1 -
2.5" of rain yesterday. Of note, QPF for the days 3 - 4 (Tue - Wed) period
has shifted quite a bit south of where it was forecast yesterday (now over
central/southern IA), and may not overlap the priming rainfall on days 1 -
2 (Sun - Mon) as much as previously anticipated, leading to an overall
decrease in the flooding potential across the region. The potential extent
of flooding impacts remains uncertain given the variable antecedent
conditions and QPF uncertainties. Nonetheless, the NWM Medium Range
Forecast (both the GFS and NBM forced) continues to show potential for
rapid onset flooding primarily across central IA, with peak flows in the
mid week time period. The previous indications for locally significant
small stream rises have dwindled, and confidence is much lower on any
potential for significant flooding. Isolated mainstem river flooding will
be possible.

.Northern Alaska...
Flooding along North Slope rivers is possible through mid week. An above
average late season snowpack combined with temperatures rising into the 60s
and 70s is expected to cause a rapid snowmelt. With ice intact on larger
rivers, ice jams could result from the snowmelt entering the rivers and
lead to sudden rises and flooding. High flows or flooding could lead to
bank erosion that could threaten nearby roads and impact access to
airstrips and low lying infrastructure. River levels are likely to crest
through early this week.

.Puerto Rico...
Urban and small stream flooding, as well as isolated flash flooding, is
possible through at least mid week due to an expected increase in daily
shower and thunderstorm activity.

//JEC

$$